This is a proposal to continue present studies aimed at establishing a link between sudden infant death syndrome (SIDS, also know as crib death) and malfunctioning autonomic reflexes. Study A is to characterize the development of autonomic function of normal term and premature infants during the first year of life. The characterization is based on by-weekly determinations of naturally occurring variations in respiratory and heart rate patterns during sleep. Since susceptibility to SIDS is greatest during the second to fourth months of life, pronounced changes in cardio-pulmonary control during this time interval will be sought. Study B is to characterize autonomic function in those high-risk infants who are hospitalized with apneic spells of unknown etiology. These infants are considered "near-miss" SIDS cases. The measures of cardio-pulmonary control for high-risk and normal infants will be compared in an attempt to determine if susceptibility to SIDS can be demonstrated.